Equilibrium molecular structure of nicotinic acid hydrazide: joint study by means of gas electron diffraction and quantum chemistry

•Nicotinohydrazide vapor was characterized by means of gas-phase electron diffraction.•Equilibrium structural parameters of the two prevailing conformers were obtained.•Structures of gaseous and solid nicotinohydrazide were found to be quite different.•Crystalline molecule was found to resemble one of high energy conformers in the gas. The conformational composition and molecular structure of gaseous nicotinic acid hydrazide (nicotinohydrazide) have been studied by means of gas electron diffraction (GED) supported by the results of quantum chemical (QC) calculations. According to QC calculations, eight conformers are possible for nicotinohydrazide. However, only two of them are in sufficient abundance to be detected by means of GED, with their ratio 7:3. Equilibrium structural parameters of the predominating conformers have been obtained with the use of anharmonic rovibrational corrections and standard enthalpy of formation of gaseous nicotinohydrazide has been calculated. The gas-phase molecular structure has been compared to the crystalline one, obtained via X-ray diffraction. Significant distinctions between the gaseous and solid structures have been revealed [Display omitted]